1. Field of the Invention
The present invention relates to an optical disc drive which records and reproduces information for an optical disc like a CD-R media or a CD-RW media.
2. Description of the Related Art
The recording format of a CD-R or CD-RW optical disc is prescribed in the Orange Book, an industry standard. The Orange Book rules dictate that data sectors which are not consecutively written require lengthy lead-in and lead-out sectors such as Link, Run-In, and Run-Out sectors. These sectors are necessary to enable optical disc drives to synchronize to the data on the optical media. This is because the laser beam must be repositioned each time a new writing session is started, and known optical disc drive positional controls are not sufficiently accurate to position a laser beam at the exact end point of previously written data.
Therefore, conventional optical disc drives need to write data on an entire track, known as Track-at-Once, or an entire disc, known as Disc-at-Once, continuously in order to avoid adding lead-in and lead-out sectors. In other words, known optical disc drives must write the entire disc or track in a single writing session.
Conventional optical disc drives employ Cross-Interleaved Reed-Solomon Code (CIRC) encoding which is performed by a CD encoder chip. The CD encoder chip automatically encodes the data in a buffer which temporarily stores data from a host while waiting for the data to be encoded and written to an optical media. Another reason that conventional optical disc drives must write data in a single session is that the CD encoder chip will continue to generate dummy data even if the buffer containing data from the host becomes empty. Continuity of data, or data succession, is lost by inserting and writing dummy data in a head where data from a preceding sector was recorded.
Because conventional disc drives need to write an entire track or disc in a single session, a problem is encountered if the flow of data from the host computer to the optical disc drive buffer is interrupted. Since CD-R and CD-RW optical discs are write-once media, a write failure results in the loss of expensive media.
The problem of maintaining data from the host in the optical disc drive buffer is severe when the writing speed of the optical disc drive is high. Because the data size of a track or disc is large compared to the optical disc buffer size, if the data transfer rate between the host computer and the optical drive is even slightly slower than the speed at which data is written to the optical disc, or data transfer between the host and the optical disc drive is interrupted for even a short period, the buffer may go empty. This problem is known as Buffer Run.
Because hosts transmit data at varying rates, some optical disc drives include a test mode that performs a dummy write operation, during which no data is actually written to the optical disc, to ensure that the transmission rate of the host is adequate to prevent buffer run. One problem with this method is that it takes twice as long to write the data to the disc. Also, because hosts sometimes encounter non-repeatable problems, the aforementioned method is not perfectly safe and the risk of losing expensive media due to buffer run errors is not completely eliminated.
Therefore, an optical disc drive that can write data consecutively and normally to an optical media in multiple sessions without the loss of data succession is needed.
Even if logical data succession is ensured as described above, data cannot be normally reproduced without physical correspondence of the succeeding portions of data written in multiple sessions.
Usually, a frame gap of up to +/xe2x88x922 bits may be present without preventing a conventional optical disc drive from properly reproducing data from an optical disc. However, if a conventional optical disc drive attempts to write multiple sessions of data by selecting a writing start point based on a rotating control by a wobble synchronic signal, a frame gap of scores of bits may result. Therefore, synchronization may be off in that portion and several frames of data may be lost.
Therefore, what is needed is an optical disc drive that is able to correctly detect an end portion of data written in a preceding write session so that an accurate write start point is provided for a succeeding write session.
Further, it is desirable that such an optical disc drive should be able to detect the end portion of data written in a preceding write session at low cost.
An object of the present invention is to provide an optical disc apparatus characterized by writing means for maintaining data succession by halting CIRC encoding at the end of a preceding write session and resuming CIRC encoding at the beginning of a succeeding write session.
A second object of the present invention is to provide an optical disc apparatus characterized by a counter circuit for counting the channel bit PLL (phase locked loop) which takes timing from the end of previously written data to select a writing start point for a succeeding write session.
A third object of the present invention is to provide a counter circuit for counting a frame sync signal which takes timing from the end of previously written data to select a writing start point for a succeeding write session.
A fourth object of the present invention is to provide controlling means for controlling the writing of data to an optical disc drive according to the present invention. The controlling means pauses a write operation when data from the host has not been transmitted in time for writing to the optical disc, and restarts the write operation when data from the host computer is again available.
A fifth object of the present invention is to provide an alternate controlling means for controlling the writing of data to an optical disc drive according to the present invention. The alternate controlling means pauses a data write operation when data from the host has not been transmitted in time for writing data to the optical disc, reduces the write speed of the optical disc drive, and then resumes the write operation.
In accordance with the first object, the optical disc drive includes a Pause circuit which masks the clock input to the encoders upon the generation of a Pause signal. This prevents the encoders from further inputting and outputting data. Therefore, even if writing to the optical disc occurs in multiple write sessions, data succession is maintained.
In accordance with the second object, one embodiment of an optical disc drive according to the present invention includes a counting circuit which counts the PLL signal derived from the channel bit. The PLL signal has the smallest error for previously written data. It is possible to calculate the end of the data based on this signal, so that the correct writing start point for succeeding data write sessions may be selected.
Many inexpensive and widely used decoder LSIs which are used in known optical disc drives do not output a channel bit PLL, but rather output a frame sync signal and a sub code sync signal as a sub code output. Therefore, in accordance with the third object, a second embodiment of an optical disc drive according to the present invention includes a counting circuit which counts a frame sync signal and a sub-code sync signal to select a writing start point for a succeeding data write session. Accordingly, it is possible to detect the end of the previously written data at low cost.
In accordance with the fourth object, one embodiment of an optical disc drive includes a processor for detecting when data from a host stored in a data buffer is low, generating a pause signal for pausing a data writing operation, waiting until additional data is received from the host, and removing the pause signal so that the data writing operation may resume.
In accordance with the fifth object, another embodiment of an optical disc drive includes a processor for detecting when data from a host stored in a data buffer is low, generating a pause signal for pausing a data writing operation, decreasing the write speed of the optical disc drive, and removing the pause signal so that the data writing operation may resume.
Because an optical disc drive according to the present invention can write in multiple sessions, a data interruption between the host and the optical disc drive does not result in the loss of the media, thereby reducing the cost of operating the optical disc drive. Accordingly, a large data buffer is not necessary, which also lowers the cost of the optical disc drive. This ability to write in multiple sessions also eliminates the need for a test write operation to test the transmission rate of the host computer, which saves time. It is also unnecessary for a user to be aware of the transmission rate of the host and the write rate of the optical disc drive, which simplifies operation of the optical disc drive.